The present invention relates generally to incandescent lighting fixtures and, in particular, to vehicle clearance and marker light assemblies for self-relamping upon the failure of such lights.
Commercial truck and trailer lighting systems are a relatively high expense maintenance item. Various laws dictate the placement and lighting characteristics of an array of marker lights and clearance lights which are required for such commercial vehicles to travel on public roads. Harsh operating conditions cause frequent failures which can be costly in terms of fines and schedule interruptions. Thus, frequent maintenance is required and is complicated and made more expensive by the large number of such lights and their relative inaccessibility.
A lamp is most prone to failure under the combined stresses of age and vibration. Therefore, a lamp will, in all probability, fail while the vehicle is in active service. Since many of the lamp assemblies must be located as much as twelve feet above the ground, the probability of a vehicle operating with one or more burned out lamps is quite high. One attempt to overcome this problem has resulted in a twin lamp assembly wherein when one lamp has burned out, the other lamp still provides a legal level of illumination.
Twin lamp fixtures typically have shock absorbent sockets for the lamps in an attempt to isolate the lamps from the various vibrations and shocks generated during operation of the vehicle. A commonly utilized lamp is a #194 which has an average "laboratory" lighting life of 1,500 hours. However, under the rigors of actual field service this life is, in reality, closer to 800 operating hours. Thus, a line-haul vehicle running for approximately eight hours per night, would require a complete clearance/marker light relamping every five months. Furthermore, since most commercial fleets relamp on an "as spent" basis, constant service attention is required to maintain a legal status and such operation is very costly. Even a minimally equipped semitrailer requires eleven light fixtures of this type, making it necessary to replace twenty-two lamps having a random failure pattern. Thus, it can be easily seen that by extending the average bulb life by a factor such as ten, the mandatory relamping cost can be reduced dramatically.
It is therefore, an object of the present invention to provide a clearance/marker light assembly which can extend the total relamping of a commercial vehicle to approximately four years.
It is another object of the present invention to provide a clearance/marker light assembly which significantly reduces the magnitude of the vibrations and shocks transmitted from the vehicle to the lamps in the assembly.
It is another object of the present invention to provide a clearance/marker light assembly which reduces the current draw by approximately one third over prior art light assemblies.